The triangle is an isosceles triangle because of its degrees. A triangle consists of 180 degrees therefore, 180-90-45 simply makes it 45 matching the other side.
So we can assume that side b is also equivalent to side a. Here we use the pythagorean theorem to find x
a^2 + b^2 = c^2
5^2 + 5^2 = c^2
25+25=50
The square root of 50 is 7.1
x= 7.1